Particle emission requirements for internal combustion engines, in particular compression-ignition internal combustion engines, are becoming increasingly stricter. As the introduction of further standards is being planned, the soot emissions downstream from the internal combustion engine, i.e., downstream from a diesel particle filter, must be monitored during the driving operation. In addition, prediction of the diesel particle filter load is to be provided for determining the soot input and optimizing the regeneration strategy or monitoring regeneration in order to ensure a high degree of system reliability for the diesel particle filter system.
Currently, resistive particle sensors for conductive particles are known in which two or more metallic electrodes are provided, the particles, in particular soot particles, which deposit on these sensors short-circuiting the electrodes meshing in a comb-like manner and thus modifying the impedance of the electrode structure. With increasing particle concentration on the sensor surface, a decreasing resistance, i.e., an increasing current at a constant applied voltage, is thus measurable between the electrodes. Normally a threshold value, a triggering threshold, is defined, and the time of accumulation is assumed as a measure for the deposited soot particle mass. For regenerating the sensor element after the deposition of soot thereon, the sensor element must usually be burned free with the aid of an integrated heating element. The sensor is unable to detect the amount of soot during the phase of being burned free.
German Published Patent Application No. 101 49 333 describes a sensor device for measuring the moisture of gases. A resistance measuring structure cooperating with a soot layer is provided on a substrate; furthermore, a temperature measuring device is provided. The temperature measuring device includes a resistance thermometer and means for measuring a frequency-dependent AC resistance. Furthermore, a heating device is associated with the sensor device. The particle size of the soot particles contained in the soot layer is between 20 nm and 150 mm.
PCT International Published Patent Application No. 03/006976 describes a sensor for detecting particles and a method for checking its function. The sensor is used for detecting particles in a gas flow, in particular for detecting soot particles in an exhaust gas flow. At least two measuring electrodes are situated on a substrate made of insulating material. The measuring electrodes are at least partially covered by a catching sleeve. A heating element is also associated with the sensor. The sensor's particle detecting function, in particular its soot detecting function, is monitored by assigning a capacitor to the measuring electrodes of the sensor and ascertaining the capacitance of this capacitor. When the capacitance of the capacitor differs from the setpoint value, an error message is generated. To burn off the deposited soot particles, the sensor is heated, and afterwards the resistance of the insulation between the measuring electrodes of the sensor is measured. The resistance of the insulation measured after heating the sensor is used as the correcting quantity for operating the sensor.